netdev - Re: [net PATCH v2] i40e/i40evf: Limit TSO to 7 descriptors for payload instead of 8 per packet

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Message-ID: <CAKgT0UeBoTEkPrvuzawh8mxZHcaFx8z-AFSG=t_=K1LmG2mthg@mail.gmail.com>
Date:	Thu, 31 Mar 2016 15:09:13 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Jesse Brandeburg <jesse.brandeburg@...el.com>
Cc:	Alexander Duyck <aduyck@...antis.com>,
	Netdev <netdev@...r.kernel.org>,
	intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Subject: Re: [net PATCH v2] i40e/i40evf: Limit TSO to 7 descriptors for
 payload instead of 8 per packet

On Thu, Mar 31, 2016 at 3:04 PM, Jesse Brandeburg
<jesse.brandeburg@...el.com> wrote:
> On Wed, 30 Mar 2016 16:15:37 -0700
> Alexander Duyck <aduyck@...antis.com> wrote:
>
>> This patch addresses a bug introduced based on my interpretation of the
>> XL710 datasheet.  Specifically section 8.4.1 states that "A single transmit
>> packet may span up to 8 buffers (up to 8 data descriptors per packet
>> including both the header and payload buffers)."  It then later goes on to
>> say that each segment for a TSO obeys the previous rule, however it then
>> refers to TSO header and the segment payload buffers.
>>
>> I believe the actual limit for fragments with TSO and a skbuff that has
>> payload data in the header portion of the buffer is actually only 7
>> fragments as the skb->data portion counts as 2 buffers, one for the TSO
>> header, and one for a segment payload buffer.
>>
>> Fixes: 2d37490b82af ("i40e/i40evf: Rewrite logic for 8 descriptor per packet check")
>> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
>> ---
>>
>> v2: I realized that I overlooked the check in the inline function and as a
>>     result we were still allowing for cases where 8 descriptors were being
>>     used per packet and this would result in 9 DMA buffers.  I updated the
>>     code so that we only allow 8 in the case of a single send, otherwise we
>>     go into the function that walks the frags to verify each block.
>>
>> I have tested this using rds-stress and it seems to run traffic without
>> throwing any errors.
>
> Looking like it is working for me too with at least the PF.

I was testing PF <-> VF in my environment so I think I ended up
covering both in my test at least.

- Alex